The Prammer system allows communication between surface equipment and downhole equipment while the downhole equipment is deployed in a well. Specifically, a “surface interface sub” communicates along communication lines comprising cable segments, high-frequency signal couplers and repeaters, among others, with downhole equipment located either close to the drill bit or anywhere else along a drill string. The drill string is comprised of many pipe joints that are connected to each other via pin-and-box rotary connections. In an embodiment of the Prammer system, the box ends contain signal repeaters that compensate for the loss of signal amplitude along the cable segments spanning the pipe joints. Signals are communicated between pipe joints via electromagnetic resonance couplers that, being passive devices, also contribute to signal loss. The signal carrier frequency is typically located in the HF-to-UHF radiofrequency range.
The surface communication sub is typically located between a drive motor in a top-drive rig and the top of the drill string. Wired or wireless interfaces may provide connectivity between the surface communication sub and the communication systems within the rig. Typically, data gathered downhole may be telemetered to the surface within a few seconds and are also within a few seconds displayed to drilling and logging personnel.
A connectivity problem occurs during tripping operations. Drill pipe frequently needs to be pulled back out of the hole and broken down in “stands” of 1-3 pipe joints that are typically racked up within the derrick for further use. Such a need may arise when the drill bit is worn out and needs a replacement or when specialized equipment needs to be included in the drill string. During tripping, the drill string is no longer connected to the drive motor and to the surface communication sub. Instead, the top of the drill string, with the box end of the current topmost drill joint pointing up, is grabbed by specialized rig equipment known as the “elevator.”
The elevator may be part of an entire “pipe handling system.” During “trip out” the drill string is speedily hoisted up into the derrick. Then, the topmost stand is disconnected from the rest of the drill string and put aside (“racked up”). The reverse procedure, “trip in” takes racked-up stands one at a time, reconnects them to the drill string, and lowers them into the well. Since the well has already been drilled to a certain depth, there is no need to connect the drive motor and the surface communication sub is also not in use during that time. Both trip-in and trip-out need to proceed as fast as possible. Long drill strings may require many hours of tripping operations that are considered unproductive since the well is not progressing.
There is a need and a desire to monitor the well during tripping and to continue gathering real-time data during that period. A portion of the well is open-hole, i.e. not cased, and therefore fragile and susceptible to damage, collapse and/or unwanted fluid ingress and/or egress. The temperatures, pressures and hole dimensions, among other parameters, should be continuously monitored along the length of at least the open-hole section. Given such data in real time or close to real time, countermeasures such as, for example, adjustments of mud densities can be initiated. In another example, hole narrowing, which may be caused by swelling clay formations, can be effectively remediated by “reaming” the affected well section, i.e. by bringing it back to proper gauge, possibly followed by an increase in mud salinity to relieve the osmotic pressure on the formation.
Hole damage may even be brought on by the tripping operation itself. The rapid removal of drill pipe causes a sudden and temporary drop in borehole pressure and a fluid suction effect (“swabbing”) develops that depends on the speed of drill pipe removal. Thus, a conflict exists between optimizing the tripping operation, i.e. minimizing the time required to remove the drill pipe, and the danger of damaging the borehole by sucking fluids and/or solids from the formation into the borehole. The maximum under pressure a formation can withstand without discharging fluids or solids into the borehole depends on the type and condition of the formation itself, and thus changes along the open-hole section of the well. It would be highly desirable to obtain at the surface a real-time reading of the actual borehole pressure close to the bit, thereby enabling the driller to optimize the tripping process, while safeguarding the integrity of the borehole and the surrounding formation.
Data gathering during tripping is called “logging while tripping” or “LWT.” LWT is traditionally memory-based, i.e. data from underground sensors are recorded in downhole memory. That memory is accessed and read out once the memory device has reached the surface during trip-out. The time delay between data gathering and data readout reduces the usefulness and validity of the data. For example, in a well, already drilled to 20,000 ft., the bottom 2,000 ft. are open-hole and require monitoring. All relevant data could be gathered in, for example, one hour. The trip-out process, however, may take, for example, another 9 hours and the data are already 10 hours old when first processed and visualized. This may be much too late in a dynamically changing environment such as an open-hole section.
The drilling process typically “over balances” the rock formation, driving native fluids away from the well. Once a coat of drilling mud has solidified on the well walls, that coat allows the native fluids to return to their original equilibrium. Monitoring this process by what is called “time lapse logging” is another important application of LWT.
There is also a need for very sensitive measurements performed downhole. Traditionally, such measurements have been reserved for wireline operations (while stopped) that provide a much quieter downhole environment than logging-while-drilling (LWD) sensor platforms. Examples include high-precision acoustic measurements and high-precision NMR measurements. In the latter, measurements of proton relaxation times may extend to several seconds, in which the NMR sensor must remain in fixed position relative to the formation. The repetitive time periods occurring in tripping, when connections are made or broken and the drill string is held in place, can be ideal time slots for such sensitive measurements.
Another downhole communication system (the “Hall system”) is described in U.S. Pat. No. 6,670,880 to Hall et al. Related to the Hall system, U.S. patent application Ser. Nos. 12/751,331 and 12/751,350, both by Veeningen et al., describe “communication interfaces” designed to provide LWT services on the Hall system. The interfaces are to be mounted on the elevator and would extend and retract carrying a Hall-style coupler. In their extended positions, the adapters would reach into the box of the topmost pipe joint such that an interface-mounted signal coupler makes physical contact with the box-mounted signal coupler. In the retracted position, the interface would get out of the way of pipe handling, allowing stands to be added or removed from the drill string.
The disadvantages of the Veeningen devices are obvious, considering that no standards exist for the design of elevators and pipe handling systems. For each rig design, the workings of the rig need to be carefully studied, following by the design and manufacturing of rig-design-specific interfaces. The interfaces are mechanically complicated and have to execute complex movements in the vicinity of fast-moving and highly automated machinery. The cables connecting the interfaces to the rig communication infrastructure are bothersome as they travel with the elevator up and down in the derrick and may get snagged and consequently ripped off.
A similar device, described by Zaleski et al. in U.S. patent application Ser. No. 13/758,406, operates stand-alone, i.e. without using the elevator as a mount. The use of the Zaleski device may be even more bothersome than the Veeningen device, as it directly interferes with the operation of the pipe handling system. At any time that the Zaleski device engages the drill string for purposes of communication, the operation of the pipe elevator must be halted. As such, the Zaleski device can be used only very sparingly and probably not at all with a highly or fully automated high-speed pipe handling system.
Therefore, a need exists for providing logging-while-tripping (LWT) services in a wired-pipe system without the need for physical access to any above-ground portion of the drill string for the purposes of retrieving data and/or to communicate with below-ground elements of the wired-pipe communication system. At the same time, the data should arrive at the surface in a timely fashion, i.e. within minutes instead of many hours as in memory-based LWT systems.
Segments of wired pipe may develop faults. These faults may be caused by the cables, by the couplers, and/or by the repeaters. It is highly desirable to detect such faults as early as possible. For example, a faulty segment, which could be a pipe joint or a stand, should not be tripped-in as it probably will render wired-pipe communication inoperable as long as the faulty segment is deployed underground. Reversely, during trip-out faulty segments should be detected as soon as they are on the rig floor, to be put aside and replaced with functioning segments.
Wired-pipe signal repeaters operate on power provided by internal batteries. It is highly desirable to detect repeaters with marginal battery charge that should not be tripped-in another time because the battery charge may not last for the entire duration of the next run. During trip-out, depleted or about-to-be-depleted repeaters should be detected as soon as they are on the rig floor, to be put aside and replaced with fresh repeaters.
Tripping operations are a highly automated and optimized work processes. It is often impossible to stop and/or to revert steps in the process. Such stopping and reversing, however, is needed in the aforementioned Hall wired pipe system in the case of communication connectivity failures in segments of the wired pipe. Although employing the Veeningen device during trip-in may detect that one or more faulty segments have been tripped-in, that information may already come too late for reversing the trip-in and replacing the faulty segment(s). Rather, trip-in typically continues and wired-pipe communication is not possible.
Testing wired-pipe segments runs into limitations on the rig floor. The pipe joints are typically assembled in stands that are racked up vertically, reaching heights of 90 feet or more. Conventional wired-pipe testing would call for sending test signals through pipe segments and measuring the attenuation of such signals. This method is more or less impossible, considering the limited access to the top end of the segment.
Therefore, a need exists to test wired-pipe segments, e.g. stands, on the rig floor, with access only to one end of each segment, before the segments are run into the hole and after segments have been pulled from the hole. Run-in could be a trip-in or a drill-forward operation. Pull-out could be a trip-out operation or may use the top-drive to rotate the drill string, in, for example, reaming operations.